Electric water heater



Dec. 3, 1968 G. c. ALDOUS 3,414,707

ELECTRIC WATER HEATER Filed Feb. 24, 1966 YFIG.I.

FIG.3.

5 RW mm m NA .N w.m m w e A 0 m m 6 WITNESSES United States Patent Oflice Patented Dec. 3, 1968 3,414,707 ELECTRIC WATER HEATER George C. Aldous, Mansfield, Ohio, assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 24, 1966, Ser. No. 529,791 4 Claims. (Cl. 219322) This invention relates to an electric water heater, and in particular to an improved immersion heating element assembly.

One common arrangement for mounting an electric resistance heating element assembly to an electric water heater tank calls for insulating the assembly from the tank and connecting a resistor between the tank and element to bleed otf corrosion currents. If the typical copper-sheathed heating element were in non-insulated relation to the tank, the substantial difference in position in the electropotential series of the copper on the one hand, and the sacrificial anode (usually magnesium) on the other hand, would result in an inordinately rapid depletion of the sacrificial anode.

An object of this invention is the provision of a heating element assembly which may be mounted in non-insulated relation upon the water heater tank without requiring the use of a bleed resistor, and which does not result in an excessively rapid depletion of the sacrificial anode provided in the tank.

Another object is the provision of such an assembly which lends itself to relatively low cost manufacture and provides other advantages with respect to the manufacturing techniques which may be employed in its construction.

In accordance with the invention, the water heater includes a conventional tank provided with the usual sacrificial anode. The heating element assembly includes the usual electric resistance heater within an outer tubular metallic sheath. The ends of the sheath are secured to and project out through a clamping or mounting plate. The sheath ends are sealed within a body of electrically insulating material which is molded and sets up in place against the exterior face of the mounting plate. The end connections of the resistance heater project out through the molded body for a connection to an electrical supply. The body of the electrically insulating material thus serves both as a hermetic seal for the ends of the sheath and as a terminal block for the end connectors. The entire heating element assembly so constructed lends itself to immersion in a tinplating solution in which the tin precipitates upon only the sheath and the mounting plate. Since the tin is less noble in the electropotential series than the typical copper sheath, the differential between the immersed part of the heater assembly and the sacrificial anode is substantially reduced, even though the heating element assembly is mounted directly and in non-insulated relation upon the tank. By molding the electrically insulating material directly to the assembly after the sheath and plate have been mechanically secured, the body of material buries the sheath ends and provides an effective seal which protects these ends during plating and handling.

The invention will be described in connection with the accompanying drawing, in which:

FIGURE 1 is a partly-broken, vertical, sectional view of a water heater according to the invention;

FIG. 2 is a horizontal sectional view corresponding to one taken along the line IIII of FIG. 1; and

FIG. 3 is an exterior face view of the assembly.

Referring to FIG. 1, the ferrous metal tank of the water heater is provided with an inner protective coating 12 of glass frit or the like. The sacrificial metal anode 14 projects into the tank and may be of any of the wellknown anodic materials such as magnesium. The heater assembly generally designated 16 may be mounted to the tank generally as shown in FIG. 1 by means of several bolts 18 which secure the clamping or mounting plate 20 to the wall of the tank 10.

The specific construction of the heater assembly according to the invention will be described mainly in connection with FIG. 2. The assembly includes the usual electrical resistance heater 22 housed in a tubular sheath 24 and maintained in spaced relation therefrom by suitable granulated insulating material 26 packed between the resistance heater and the sheath. The mounting plate 20, which preferably is a steel plate of substantial thickness and relatively fiat, is provided with a pair of openings 28 which receive the end portions of the sheath. The extreme ends of the sheath preferably project out past the exterior face of the mounting plate. The terminal portions of the sheath may be mechanically secured to the mounting plate by a staking operation in which the metal around the openings 28 through which the sheaths are received is deformed sufiiciently to hold the sheath in place relative to the plate. The connector ends 30 of the internal resistance heater 22 project out substantially beyond the ends of the sheaths.

After the sheaths have been mechanically secured to the mounting plate 20, the plastic terminal block 32 is molded in place directly against the exterior face of the plate. The mold for forming the terminal block is placed in encompassing relation to the projecting ends of the sheath. The mold may be of single cavity form, lined with silastic rubber for a quick release, and placed directly against the exterior face of the plate. The insulating plastic material, such as an epoxy resin, is poured into the mold and, after it sets, the mold may be readily removed for reuse.

The heating element assembly is then immersed in an electroplating solution of a material such as tin. The plate 20 and the exposed portions of the sheath 24 become coated with tin, which is indicated by the numeral 34 in FIG. 2. The tin does not coat the plastic block 32 or the projecting ends 30 of the heater terminals since they are insulated from the sheath and block and do not carry a charge effecting plating. By virtue of the lack of precipitation of the tin upon the block 32, and the hermetic seal afforded by the block 32, no special steps must be taken during the plating process to protect against electric shorting paths being established between parts which are ultimately in insulated relation. Accordingly, handling of the assembly for plating is simplified. Also, by virtue of the entire assembly being plated as an integral unit, damage to the plating from extra handling is minimized.

The exemplary material tin, stated as the presently preferred coating material for the heating element assembly, occupies a position of less nobility in the electropotential series of metal than copper which, being relatively inexpensive, is preferred as a sheath material. Accordingly, since the gap in the electropotential series between the magnesium anode and the tin material on the heater assembly is less than the gap between magnesium and copper, in service the magnesium anode will not be depleted at an excessively rapid rate, even though the plate 20 is mounted directly to and in non-insulated relation upon the tank 10. In addition to the tin-plating reducing the electropotential gap and accordingly prolonging the life of the anode, the tin plating on the steel mounting plate protects the plate from rust and corrosion.

The block 32, in addition to hermetically sealing the sheath ends and providing a hermetic seal between the mounting plate and sheath junctures, also supports the terminal end connectors 30 and provides electrical clearance between the end connectors and other parts.

It will be appreciated that the term copper includes copper alloys, and the term tin includes tin alloys.

Having described my invention I claim:

1. An electric Water heater comprising:

a tank having a protectively coated interior;

a sacrificial metal anode in said tank;

a heating element for immersion in said tank, said heating element including a tubular metallic sheath about an internal, insulated resistance element having opposite end connectors projecting out of the respectively opposite ends of said sheath;

a mounting plate for said heating element including a pair of openings receiving said opposite ends of said sheath in through projecting relation;

means mechanically securing said sheath to said plate;

a body of electrical insulating material molded in place on the exterior face of said plate to encompass said sheath ends with said end connectors projecting out of said body; and a coating of metal, less noble in the electropotential series than said sheath metal, covering said sheath and said mounting plate.

2. A heater according to claim 1 wherein: said sheath material is copper and said metal coating on said sheath and mounting plate is tin.

3. A heater according to claim 1 wherein: said sheath ends terminate beyond the exterior face of said plate and are buried in hermetically sealed relation in said insu1ating material body.

4. A heater according to claim 1 wherein: said mounting plate is a single relatively thick steel member mounted directly upon said tank in electrically non-insulated relation to said tank.

References Cited UNITED STATES PATENTS 2,274,445 2/1942 Greer 2l9523 2,860,227 11/1958 Fox. 2,947,846 8/1960 Fox. 2,951,929 9/ 1960 FOX. 3,060,112 10/1962 Shornber 204197 RICHARD M. WOOD, Primary Examiner. C. L. ALBRITTON, Assistant Examiner. 

1. AN ELECTRIC WATER HEATER COMPRISING: A TANK HAVING A PROTECTIVELY COATED INTERIOR; A SACRIFICIAL METAL ANODE IN SAID TANK; A HEATING ELEMENT FOR IMMERSION IN SAID TANK, SAID HEATING ELEMENT INCLUDING A TUBULAR METALLIC SHEATH ABOUT AN INTERNAL, INSULATED RESISTANCE ELEMENT HAVING OPPOSITE END CONNECTORS PROJECTING OUT OF THE RESPECTIVELY OPPOSITE ENDS OF SAID SHEATH; A MOUNTING PLATE FOR SAID HEATING ELEMENT INCLUDING A PAIR OF OPENINGS RECEIVING SAID OPPOSITE ENDS OF SAID SHEATH IN THROUGH PROJECTING RELATION; MENS MECHANICALLY SECURING SAID SHEATH TO SAID PLATE; A BODY OF ELECTRICAL INSULATING MATERIAL MOLDED IN PLACE ON THE EXTERIOR FACE OF SAID PLATE TO ENCOMPASS SAID SHEATH ENDS WITH SAID END CONNECTORS PROJECTING OUT OF SAID BODY; AND A COATING OF METAL, LESS NOBLE IN THE ELECTROPOTENTIAL SERIES THAN SAID SHEATH METAL, COVERING SAID SHEATH AND SAID MOUNTING PLATE. 